The latest generation of DNA sequencing technology has spurred a tremendous increase in the use of sequencing to answer fundamental questions in biology and medicine. Whole-genome sequencing is being used to study cancer, to study common disease-causing variants in the human genome, and to create a better picture of human diversity. Sequencing of messenger RNA through the protocol known as RNA-seq has led to an explosion of projects to characterize the transcriptome of many cell types in many species. These sequencing-based studies generate enormous amounts of data, which in turn require sophisticated, efficient computational tools to align the DNA sequence back to a reference genome and to help interpret the results. Our group has developed a suite of software tools for alignment of DNA and RNA to a reference genome. These include Bowtie, a very fast short-read alignment program; TopHat, an alignment program that aligns spliced transcripts (mRNA) across introns; and Cufflinks, a program that assembles complete transcripts, including alternative splice variants, from the alignments that TopHat produces. Our tools have been designed to handle very large next-generation sequence data sets, reducing alignment times that took multiple CPU-days with previous tools to just minutes. They also have relatively modest memory requirements, allowing them to be run on a desktop computer. For these and other reasons, these programs have become the preferred tools for numerous research groups; the Bowtie program alone has already attracted a very large user base, with over 20,000 downloads since its initial release in 2008. In this proposal, we ask for support to maintain these open-source software programs, adapt them to continuously changing DNA sequencing technology, and add new features designed to improve the alignments and to assist investigators with their analyses.